This invention relates generally to an encryption process for a remote keyless entry system and, more particularly, to an encryption process for a remote keyless entry system that includes a rolling code updating scheme that provides heightened security integrity against unwanted entry.
Vehicle remote keyless entry system that enables a vehicle operator to perform Certain functions, such as lock or unlock a door or trunk of the vehicle, from a remote location are known in the art. Keyless entry systems of this type generally include a portable transmitter carried by the vehicle operator, usually included as part of a fob attached to a key chain for carrying keys of the vehicle. The transmitter will include a button that, upon activation, will cause the transmitter to broadcast a radio frequency signal as a series of coded data bits. If the vehicle is within the operating range of the transmitter, an antenna and receiver associated with the vehicle will receive the coded signal. If the receiver determines the coded signal to be valid, then the receiver will automatically cause the desired function to be performed as encoded on the signal. A more complete discussion of remote keyless entry systems of this type can be found in U.S. Pat. No. 4,942,393, issued Jul. 17, 1990, and assigned to the assignee of this invention.
Because of at least the advantage of convenience that is attributable to controlling vehicle functions in this manner, keyless entry systems are becoming increasingly more common for use in remotely unlocking or locking vehicle doors as the vehicle operator approaches or leaves the vehicle. As more and more vehicles are being equipped with keyless entry systems, the occasions where vehicle thieves are attempting to duplicate the coded transmissions to gain access to the vehicle are also increasing. Consequently, it has become necessary to incorporate more rigorous encoding techniques for coding the transmitted signal to prevent potential thieves from gaining access to the coded transmission signal.
One method in which a potential thief can gain knowledge of the coded transmission is by recording the transmitted signal after the vehicle operator has activated the transmitter. The thief can then play the recorded signal back at a time when the operator is not in the vicinity of the vehicle in order to fraudulently gain access to the vehicle. In order to prevent a previously recorded transmission from being a valid signal, it is known to use encoding techniques that provide rolling codes so that the signal code changes with each transmission. In these types of systems, the receiver must also systematically update its code so as to be able to synchronize with the transmitter signal.
The availability of sophisticated recording devices and cryptanalysis algebraic techniques that can readily be implemented with portable computers make it increasingly possible for professional thieves to break conventional rolling codes. In particular, it is possible to decipher many rolling codes by recording successive transmissions from a transmitter, thereby enabling a thief to anticipate future valid codes. Further, advanced transmitting devices are capable of transmitting large numbers of sequential codes over relatively short periods of time. Therefore, schemes can be devised to update a transmitted signal in a systematic manner in order to eventually hit on the right combination of coded bits.
Accordingly, it is an object of the present invention to provide an encoding technique that generates a rolling code for use in a keyless entry system for a vehicle that will prevent unwanted entry of the vehicle by recording the coded transmission.
It is a further object of the present invention to provide an encoding technique that is adaptable to update a rolling code used in a keyless entry system for a vehicle that will prevent unwanted entry of the vehicle by recording and analyzing a series of successive coded transmissions even if a code breaker uses sophisticated cryptanalysis algebraic techniques.
It is also an object of the present invention to provide an encoding technique that is adaptable to update a rolling code used in a keyless entry system for a vehicle that will prevent unwanted entry of the vehicle even if the coding encryption and decryption algorithms are in the public domain.
It is yet another object of the present invention to provide an encoding technique that is adaptable to update a rolling code used in a keyless entry system for a vehicle that will prevent unwanted entry of the vehicle by random successive coded transmissions over a reasonable period of time.
In accordance with the teachings of the present invention, a rolling code encryption process for a remote keyless entry system is disclosed. The encryption process makes use of a command code shift register, a security code shift register, and a sequence code shift register for establishing a series of encoded data bits where the data bits are transmitted from a portable transmitter to a receiver associated with a vehicle in order to perform a certain function remotely from the vehicle, such as unlock or lock the vehicle's door. The command code shift register provides the portion of the transmitted data bits that define the function to be performed. The sequence code shift register provides the portion of the transmitted data bits that continually updates a sequence number so as to enable the receiver to be synchronized with the transmitter. In a preferred embodiment, neither the command code data bits nor the sequence code data bits are encrypted.
The security code shift register provides the portion of the transmitted data bits which is encrypted in a rolling manner so as to prevent a would-be code breaker from gaining knowledge of the transmitted signal. The encrypted bits in the security code shift register are set by a first and second pseudo random number generator. The first and second pseudo random number generators each include a shift register whose bits are set by exclusively NORing a tap bit location of the shift register with an end bit location of the shift register. The tap bit locations are selected so as to maximize the number of bit sequences that can be generated before the series will repeat itself. Predetermined bit locations from the shift registers associated with the pseudo random number generators are exclusively ORed together, and the outputs of the OR gates set the individual bits in the security code register. The shift registers are cycled after each transmission a number of times depending on the contents of the shift register in order to reset them to a new code pattern before the shift registers are exclusively ORed together. In this manner, the security code register is updated each time the transmitter is activated.
Additional objects, advantages, and features of the present invention will become apparent from the following description and appended claims, taken in conjunction with the accompanying drawings.